The Syrian state news agency said warplanes hit rebel positions around Aleppo after Syrian opposition fighters said they had broken a three-week government siege of the devastated city.

The battle for Aleppo, once Syria's largest city, is turning into a pivotal moment in the five-year civil war that has ravaged the country, killing hundreds of thousands and displacing more than 1 million people.

An alliance of more than two dozen rebel groups united to push government forces and allied fighters out of parts of the southern Ramouseh district on August 6.

If their advance holds, it would allow for supplies to be delivered to some parts of the city, and it would dent the Syrian regime's confidence, which has been bolstered by Russia's air campaign.

The SANA news agency denied that the government siege of Aleppo had been broken, and said warplanes were hitting rebel positions and vehicles.

The media arm of Hizbullah, the Lebanese Shi'ite militant group fighting alongside the Syrian government, conceded the rebels' advance, adding that air strikes leveled one of the military colleges after forces withdrew.

The Syrian Observatory for Human Rights was quoted by the AFP news agency as saying that a road opened to the south of Aleppo was too dangerous for civilians to use, and that intermittent clashes and air strikes were taking place.

Opposition fighters and militant Islamists have waged fierce assaults in the past week to end the siege, which had been in place since July 17, trapping an estimated 250,000 civilians in Aleppo’s eastern districts.

The rebel advance also threatens a major highway linking the government-controlled part of Aleppo to the outside world. That puts an estimated population of 1.2 million at risk of losing a supply line.